1. Field of the Invention
The present invention relates to an improved hybrid solar/combustion powered receiver for providing thermal energy for use such as, for example, by a hot gas engine.
2. Description of the Prior Art
"Solar only" receivers typically function to convert solar radiation to heat energy for use, for instance, in hot gas engines e.g. of the Rankine, Stirling, or Brayton types or another apparatus requiring thermal energy input. "Hybrid" receivers typically have the solar energy input augmented and/or supplanted by an auxilliary energy source, such as combustion of natural gas, for use during periods of darkness or periods of low insolation (e.g. cloudy days).
A conventional hybrid solar/gas powered receiver is that proposed in the "Dish Stirling Solar Receiver Program Final Report", document No. ER 79917-3, Dec. 15, 1980, drawing No. 79917001. That receiver included a generally cylindrical insulated housing with an aperture at one axial end and a conical heat exchanger at the other axial end. The heat exchanger, in particular, was formed from a plurality of tubes partially imbedded in a gas-impermeable solid metal substrate to form the conical heat exchanger against which the solar radiation impinged. A plurality of gas burners were mounted in the housing wall to direct hot combustion gases to impinge on the rear, or un-illuminated, side of the conical heat exchanger, and between portions of the heater tubes connecting the regenerator to the conical heat exchanger. In this prior art hybrid receiver, the conical heat exchanger itself prevented the escape of combustion gases through the aperture during gas power operation. Also, the subject prior art hybrid solar receiver was used in conjunction with a Stirling-type hot gas engine for the conversion of the thermal energy into mechanical power.
Several of the shortcomings with the subject prior art hybrid receiver were thermal stress cracking of the heater tubes imbedded in the solid metal substrate, which was induced by the extreme rigidity of the solid conical heat exchanger design and poor heat transfer from the combustion gases during gas power operation. The present invention attempts to overcome these problems by providing a hybrid receiver having good combustion gas heat transfer characteristics, as well as good solar radiation heat transfer characteristics, while continuing to prevent the escape of combustion gases and the resulting loss of overall receiver efficiency.